The present invention relates to an apparatus for growing a single crystal of a semiconductor compound by using a horizontal zone melt technique, and more particularly to an apparatus for growing a single crystal of a semiconductor compound of Group III-V or Group II-VI such as GaAs, InP, or CdTe by using a horizontal zone melt technique.
At the present time, a horizontal Bridgman method and a liquid encapsulated Czochralski method are generally used as a practical method for growing a single crystal in manufacturing GaAs wafers.
In these methods, the entire single crystal growth procedure is carried out at high temperature of at least 1,238.degree. C., that is, the melting point of GaAs. Consequently, they have a disadvantage that unnecessary residual impurities are inevitably present in final products, in that the GaAs melt is continuously maintained in contact with a reaction container at high temperature.
Furthermore, when impurities such as In or Si are added for the purpose of lowering the dislocation density in crystals, inherent segregation coefficients of respective impurities result in a relatively increased difference between the concentration of impurities at the beginning of the growth and the concentration of impurities at the end of the growth. In result, there is a problem of poor uniformity in the direction of crystal growth, which causes poor uniformity of electrical properties in the crystals. This poor uniformity of electrical properties in the direction of crystal growth lowers the yield of the growth, thus it is required to provide an improvement therein. Considering that the problem of lowering the yield is caused by the poor uniformity of the growth encountered in the above-mentioned horizontal Bridgman method and liquid encapsulated Czochralski method, a horizontal zone melt technique for growing crystals is noticeable as a technique for increasing the yield of the crystals.
The horizontal zone melt technique had been initially proposed by J. L. Richard in conjunction with the growth of single crystals of GaAs [Please refer to J. L. Richard, J. Appl. Phys, 31,600 (1960)]. In this horizontal zone melt technique, the GaAs melt is locally present, so that the penetration of impurities into a reaction container or tube containing the melt can be minimized. Accordingly, the concentration of the impurities is uniformly maintained in the direction of crystal growth, thereby enabling the yield of crystals to be increased. Recently, application of this technique has been extended to the manufacture of wafers with a relatively large diameter, for example, up to 3 inch [please refer to S. Mizuniwa, M. Kashiwa, T. Kurihara and S. Okubo, Hitachi Cable Rev. No. 7,51 (1988)].
However, conventional single crystal growers using the above-mentioned horizontal zone melt technique use mostly an electric ceramic furnace which is disposed at the high temperature section of each grower, whereby it is difficult to effectively form a flat temperature profile zone at the high temperature section. Furthermore, the entire procedure of single crystal growth cannot be practically observed. In result, it is difficult to grow single crystals reproducibly.